In an electronic timepiece of high accuracy, a quartz crystal oscillator is generally employed as a time-standard signal generator. As is well known, the frequency generated by the quartz crystal oscillator changes with ambient temperature. Accordingly, in order to maintain the high accuracy of such an electronic timepiece, it is necessary to compensate for the change in the oscillation frequency of the quartz crystal oscillator or to adjust the divider frequency. Conventionally, the frequency has been compensated for temperature variations by providing in the quartz crystal oscillating circuit a capacitance element which is sensitive to temperature or by the use of a similar circuit element. The temperature characteristic of the circuit element thus compensates for the frequency-temperature characteristic of the quartz crystal oscillator. However, for this arrangement to be effective, the temperature-frequency characteristic of the quartz crystal oscillator must be exactly opposite to that of the added circuit element. As is evident, it is difficult to find a circuit element which will exactly compensate for the frequency-temperature characteristic curve of the quartz crystal oscillator. Moreover, the temperature-frequency characteristic curve of both the oscillator and of the compensation element change with time so that even if a circuit element having the desired properties were available, the process of aging would seriously degrade the accuracy of the combination.
In my Japanese Patent Application No. 81375/76 filed in Japan on July 7, 1976, and also filed in the United States on July 7, 1977, U.S. Ser. No. 813,732, (now U.S. Pat. No. 4,142,360, issued Mar. 6, 1979) I have described a temperature compensating device comprising a first oscillator for generating time standard signals and a second oscillator for detecting the temperature, the second oscillator having a different temperature characteristic from that of the first oscillator. The combination of the two oscillators makes it possible to determine the ambient temperature and to effect temperature compensation during frequency division. While effective, this construction suffers from difficulties in combining quartz crystal oscillators, and, particularly, with respect to aging.
As is evident, it would be desirable to provide circuitry for an electronic timepiece wherein the frequency is kept stable over long periods of time despite changes in ambient temperature and wherein timing adjustment can readily be effected both at the time of manufacturing and during repair of the timepiece.
A further point to be taken into consideration is that in conventional multi-functional timepieces, when it is desired to increase the number of functions which the timepiece can carry out, circuits must be redesigned, so that whenever product models are changed and new models are developed, a substantial expense both in time and costs must be paid. Moreover, where the display means for such a timepiece is of the seqment type, the number of multiple functions which can be displayed is severely limited.
What is needed is an electronic timepiece which can be adapted to perform many supplemental functions without redesign of the basic circuits.